Multicellular tissues, and the stem cells that renew them, continuously experience and exert mechanical forces. Although applied force is known to direct stem cell behavior in culture, the role of physiological forces in regulating stem cells witin organs is little explored. Elucidating these roles in a simple invertebrate organ will reveal basic information about the in vivo mechanobiology of stem cells and lay groundwork for future studies in more complex systems. The midgut of adult Drosophila provides such a reductionist system. The epithelium of this digestive, tube-shaped organ is continually renewed by resident stem cells, highly genetically tractable, and amenable to live imaging. Taking advantage of these features, the long-range goal of this research is to understand how stem cells exert and respond to mechanical force during midgut epithelial renewal and tumorigenesis. The central hypothesis of this proposal is that stem cell divisions are sensitive to epithelial tension forces, and that altered responses to these forces underlie stem cell-driven tumorigenesis. To investigate this hypothesis, an interdisciplinary strategy will be used that combines molecular tension sensors, targeted manipulation of actomyosin contractility, and biophysical modeling of cellular mechanics. First, the mechano-sensitivity of normal stem cell divisions will be ascertained by examining real-time dynamics of E-cadherin based tension forces around dividing stem cells, determining how force dynamics and division behavior change when actomyosin contractility is perturbed, and evaluating the long-term impact of perturbed contractility on epithelial renewal. Second, the mechano-sensitivity of tumor-generating stem cells will be assessed by applying similar experimental strategies to stem cells lacking the Notch tumor suppressor, and examining early and late stages of tumor growth. Third, guided by the outcomes of these experiments, computational models will be developed to simulate the roles of tension forces during normal and tumor-generating stem cell divisions. By modeling mechanical feedback and different sources of tension force in silico, new hypotheses will be generated to direct future investigation. The study design has high research training potential because it enables the acquisition of wet lab proficiency while expanding prior skills in computational modeling. Altogether, the proposed work will provide new knowledge of how epithelial tension forces influence divisions of midgut stem cells during renewal and tumorigenesis, advancing understanding of the mechanobiology of epithelial stem cells in vivo.